Due to request for low abrasion on rotational elements to achieve an extended life and for low extent of noise, fluid dynamic bearings (FDB) have been used in conventional fan motors.
FIG. 4 depicts an FDB unit in which a shaft 80 extends through a bearing sleeve 81 with a clearance space formed therebetween. The clearance space is filled with lubricant oil that provides a medium through which a dynamic fluid pressure field may be generated. Relative rotation between the bearing sleeve 81 and the shaft 80 is required to set up the dynamic fluid pressure field. The bearing sleeve 81 supports radial load by metal-to-metal contact when there is no relative motion. During normal operation, the spinning of the shaft 80 sets up a steady pressure field around the clearance space that pushes the shaft 80 and the bearing sleeve 81 apart and thus prevents metal-to-metal contact. To obtain an improved dynamic pressure field, grooves 82 are formed on the inner surface of the bearing sleeve 81.
The bearing sleeve 81 is disposed in a housing 83. A ventilating passage 85 is formed between the outer periphery of the bearing sleeve 81 and an inner surface of the housing 83. The ventilating passage 85 has a vertical section and a horizontal section. This ventilating passage 85 allows air to escape the bearing sleeve 81 when the shaft 80 enters the bearing sleeve 81. However, the fluid dynamic bearing system is cooperatively formed by two components, i.e., the housing 83 and the bearing sleeve 81. To ensure the dynamic fluid pressure, the two components must be precisely produced and then assembled together. This structure is complicated and necessitates a high manufacturing cost.
For the foregoing reasons, there is a need for a fluid bearing having a simple structure with low cost.